1. Field of the Invention
The invention relates to optical communication systems particularly with respect to switching optical data signals between optical channels with high speed and low insertion loss.
2. Description of the Prior Art
Many mechanisms are known in the prior art selectively switching an optical information signal between two or more optical channels. For example, mechanical devices are utilized that selectively position an output face of an optical fiber adjacent input faces of plural optical fiber output channels for switching the input optical signal to selected optical output channels. Other mechanical devices include positionable mirrors and lenses to switch the light beams among the channels. Such mechanical devices, including the motive means thereof, tend to be unacceptably slow in operation for use in optical communication systems, as well as tending to be unreliable and bulky.
The prior art also contemplates non-mechanical switching arrangements utilizing an electro-optic effect or an acoustic-optic effect. Such prior art optical switches which utilize diffraction tend to lose optical intensity into the side lobes thereof resulting in less signal into the intended output channel. Such switches utilizing diffraction methods also tend to deflect a portion of the optical signal into non-selected output channels resulting in non-zero extinction ratios for these channels. In the prior art optical switches utilizing the electro-optic effect, the light signal is coupled into and out of a lossy electro-optic medium thereby introducing undesirably high insertion losses.
Another disadvantage of the prior art optical switches is that, generally, a stable electronic signal must be maintained for the switched and unswitched states of the devices. For example, in electro-optic switches a controlled voltage must be applied to change output channels. Thus, such electro-optic switches require precision voltage control circuitry. In the prior art acousto-optic switches, a controlled electronic frequency signal is required for diffraction of the light in the desired direction. Thus, such acousto-optic switches require a precise electronic frequency signal generator.